VII. SYNTHESIS OF RNA AND RIBOSOMES 343 



or all rihosoines can be measured. Furthermore, there may be no im- 

 mediate alteration in the flow if some of the products are faulty and 

 nonfunctional. In contrast, the experiments dealing with information 

 usually measure one particular function such as an enzymic activity 

 and the rate of synthesis of the particular functional enzyme may differ 

 markedly from the average rate of protein synthesis. 



B. CORREL.\TION WITH ENZYME INDUCTION 



Upon addition of the inducer the rate of synthesis of the enzyme 

 /8-galactosidase increases 200-fold. The time constant of the induction 

 process is as low as 2Y2 minutes when the inducer level is high. As the 

 same time constant appears in the kinetics of "deinduction" when the 

 inducer is diluted out it seems reasonable to attribute the kinetic char- 

 acteristics to the formation and subsequent decay of unstable enzyme 

 forming units (Pardee and Prestidge, 1961; Boezi and Cowie, 1961). 



Attributing all of the increase in synthetic rate to an increase in the 

 number of enzyme-forming units (EFU), and assuming that there is 1 

 EFU per cell before induction, the number of EFU's is about 200/cell in 

 fully induced cells. This number is not unreasonable since ^-galactosi- 

 dase constitutes 2% of the protein and its synthesis might be expected 

 to involve 2% of the cells' 15,000 70S ribosomes. As the time constant 

 for induction is 2Y2 minutes, the initial rate of synthesis must be 1.3/ 

 sec/cell in order to build up a complement of 200/cell in this time. Since 

 the rate of 70S ribosome synthesis is 3/sec/cell (15,000/cell, 0.02%/ 

 sec) the cell could supply completely new ribosomes at the required 

 rate but only by devoting nearly half its capacity for ribosome synthe- 

 sis to that particular product. Furthermore, if the de novo synthesis 

 of complete 70S particles were required, the kinetics of induction might 

 be expected to show the somewhat longer delay characteristic of the 

 appearance of new material in finished ribosomes. 



On the other hand, one RNA unit of the eosome fraction might be 

 sufficient to act as template. The minimum number of eosomes synthe- 

 sized is 36/sec/cell (MW = about 0.15 X 10", degradation ignored) and 

 the number needed for /?-galactosidase EFU's would be 3.6% of the 

 total. Furthermore, the kinetics of formation of ^-galactosidase EFU's 

 correspond to the kinetic of eosome formation. 



The average molecular weight considered is of course too small to 

 specify a protein molecule of 100,000 MW. Perhaps the RNA used as 

 template for yS-galactosidase is considerably larger than the average, or 

 perhaps only a part of the enzyme molecule is dependent upon induc- 

 tion for its synthesis. 



In any event the part of the DNA associated with /3-galactosidase 



